Scientific Method —

X-rays highlight the power source produced by a supernova

Radioactivity from unstable titanium powers the afterglow of supernova 1987a.

A ring of bright material surrounds the supernova remnant SNR 1987a, the closest supernova to Earth in 400 years. New observations have shown that much of the light emitted from the remnant is due to the decay of radioactive titanium.

Supernova 1987a stands as the best-studied explosion of its type. Thanks to its location in the nearby galaxy known as the Large Magellanic Cloud (LMC), astronomers have been observing it starting with the first moments after the explosion. As a result, its remains provide some of the best tests of our ideas about supernova explosions, which produce and distribute many of the heavy elements required for planet formation and life.

But a number of the elements typically synthesized in supernovae are unstable and decay over the months and years that follow, filling the debris remnant with energy and keeping it bright long after the energy from the initial explosion has dissipated. In particular, the decay of a radioactive isotope of titanium produced generated in supernova remnants is thought to be responsible for much of the optical, infrared, and ultraviolet light astronomers record. New X-ray observations have now revealed the decay of titanium in a supernova directly, and found it to be sufficient to power much of the emission in the years immediately following the explosion.

S. A. Grebenev, A. A. Lutovinov, S. S. Tsygankov, and C. Winkler also found there was more titanium in the supernova remnant SNR 1987a than expected from theory. Though the range of possible values overlapped the theoretical maximum, the authors suggested it may be necessary to reexamine details in the physical models of nuclear fusion during supernova explosions. These results provided the best data so far for the physical conditions in supernova remnants, including how they produce and disperse heavier elements into interstellar space.

While much of the Universe's hydrogen, helium, and lithium were produced in the earliest minutes after the Big Bang, all other elements were birthed by stars. Some of these elements were fused during the star's life, but others were forged during explosions of the heaviest stars (those more than 8 times the mass of the Sun). These explosions provided many of the raw ingredients for planets like Earth and later generations of stars.

Spreading the nuclear love

The explosions of very massive stars are known as core-collapse supernovas. The second major type of supernova, known as type—Ia, are related to the explosion of white dwarfs; these supernovas also produce and disperse heavy elements. The third method for distributing the raw materials for new generations of stars and planets is much gentler: when stars like the Sun die, they shed their outer layers gradually. Even though stars like these don't fuse heavy elements, they still contain some of them, relics of earlier stellar cycles.

In the first few years after the explosion, most of the light in a supernova comes from radioactive cobalt (in the isotopes 56Co and 57Co). These decay into an isotope of titanium (44Ti), which itself is unstable, decaying into lighter elements over time. This decay process keeps the supernova remnant hot, and powers the emission of much of the ultraviolet, visible, and infrared light. This keeps the material bright until years pass and the expanding shells of ejected matter collide with gas in interstellar space. This collision can ultimately end up outshining the remnant itself.

The decay of 44Ti produces high-energy X-ray photons at three distinct wavelengths. The researchers in the current study aimed the INTEGRAL (INTErnational Gamma-RAy Laboratory) satellite at SNR 1987a for about 4.5 million seconds (a total of over seven weeks) to obtain clear X-ray spectra. This process was complicated by the presence of a pulsar and a black hole binary system that, from our perspective, appear near SNR 1987a in the sky—these bodies also emit X-ray light. The astronomers identified the telltale spectral signature of titanium decay, and extrapolated from the number of photons (the flux) to determine the mass of the titanium before the decay process began.

The mass actually exceeded the amount predicted from theory, though the range of possible values in their estimates include the maximum expected value based on predictions. This was a little surprising, since the only other supernova remnant with measured titanium emission (Cassiopeia A) showed far less. However, supernova 1987a was exceptional: the progenitor star was a massive blue star, as opposed to the red stars that comprise most supernovas. As a result, its explosion could have followed a slightly different path than theory predicted; the authors suggested investigating this possibility.

Supernova explosions are physically complicated systems, both from a theoretical and observational point of view. Detailed observations such as this allow astronomers to refine their models, to understand how chemical elements are synthesized and dispersed as stars die.

<quote>Thanks to its location in the nearby galaxy known as the Large Magellanic Cloud (LMC), astronomers have been observing it starting with the first moments after the explosion. </quote>

Uhh, in a similar vein to above, I don't think so! Since SN 1987A is approximately 168,000 LY away, it blew up before a telescope ever existed here on Earth or was ever trained upon the heavens. Perhaps it has been studied starting with the first moments after the radiation from the explosion arrived here on Earth ;-).

<quote>Thanks to its location in the nearby galaxy known as the Large Magellanic Cloud (LMC), astronomers have been observing it starting with the first moments after the explosion. </quote>

Uhh, in a similar vein to above, I don't think so! Since SN 1987A is approximately 168,000 LY away, it blew up before a telescope ever existed here on Earth or was ever trained upon the heavens. Perhaps it has been studied starting with the first moments after the radiation from the explosion arrived here on Earth ;-).

The photons we are seeing don't know that though. To them it literally just happened.

<quote>Thanks to its location in the nearby galaxy known as the Large Magellanic Cloud (LMC), astronomers have been observing it starting with the first moments after the explosion. </quote>

Uhh, in a similar vein to above, I don't think so! Since SN 1987A is approximately 168,000 LY away, it blew up before a telescope ever existed here on Earth or was ever trained upon the heavens. Perhaps it has been studied starting with the first moments after the radiation from the explosion arrived here on Earth ;-).

The photons we are seeing don't know that though. To them it literally just happened.

Photons think that everything that happens to them happens in an instant. They're just dumb - or we're fooling ourselves.

<quote>Thanks to its location in the nearby galaxy known as the Large Magellanic Cloud (LMC), astronomers have been observing it starting with the first moments after the explosion. </quote>

Uhh, in a similar vein to above, I don't think so! Since SN 1987A is approximately 168,000 LY away, it blew up before a telescope ever existed here on Earth or was ever trained upon the heavens. Perhaps it has been studied starting with the first moments after the radiation from the explosion arrived here on Earth ;-).

The photons we are seeing don't know that though. To them it literally just happened.

Photons think that everything that happens to them happens in an instant. They're just dumb - or we're fooling ourselves.

Since we have been observing it from 1987, I'd love to see a time lapse movie of the explosion ... Found it. ...

The time-lapse starts in 1994, well after the initial explosion. Unfortunately, I doubt we have any decent images of the star before it went supernova. It's a pretty big sky and there wasn't anything interesting about it until it blew up.

Still, it's an interesting series of images. Thanks for posting the link.